﻿namespace Molten;

public class PerlinNoise
{
    // Inner class to speed up gradient computations
    // (array access is a lot slower than member access)
    private struct Grad
    {
        public double x, y, z, w;

        public Grad(double x, double y, double z)
        {
            this.x = x;
            this.y = y;
            this.z = z;
            this.w = 0;
        }
    }

    private Grad[] grad3 = new Grad[] {
    new Grad(1,1,0), new Grad(-1,1,0), new Grad(1,-1,0), new Grad(-1,-1,0),
    new Grad(1,0,1), new Grad(-1,0,1), new Grad(1,0,-1), new Grad(-1,0,-1),
    new Grad(0,1,1), new Grad(0,-1,1), new Grad(0,1,-1), new Grad(0,-1,-1)
};

    private short[] p;/* = new short[] {
		151,160,137,91,90,15,131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,190,6,148,
		247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,88,237,149,56,87,174,20,125,136,171,168,68,175,
		74,165,71,134,139,48,27,166,77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,102,143,54,
		65,25,63,161,1,216,80,73,209,76,132,187,208,89,18,169,200,196,135,130,116,188,159,86,164,100,109,198,173,186,3,64,
		52,217,226,250,124,123,5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,223,183,170,213,
		119,248,152,2,44,154,163,70,221,153,101,155,167,43,172,9,129,22,39,253,19,98,108,110,79,113,224,232,178,185,112,104,
		218,246,97,228,251,34,242,193,238,210,144,12,191,179,162,241,81,51,145,235,249,14,239,107,49,192,214,31,181,199,106,157,
		184,84,204,176,115,121,50,45,127,4,150,254,138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180
	};*/

    // To remove the need for index wrapping, double the permutation table length
    private short[] perm = new short[512];
    private short[] permMod12 = new short[512];

    public PerlinNoise(long seed)
    {
        p = new short[256];
        Seed(seed);
    }

    /// <summary>(Re)seeds the instance with the provided seed.</summary>
    /// <param name="seed">Seed.</param>
    public void Seed(long seed)
    {
        RandomNumber rnd = new RandomNumber(seed);
        GeneratePermutations(rnd);
    }

    /// <summary>(Re)seeds the instance with a random seed.</summary>
    public void Seed()
    {
        RandomNumber rnd = new RandomNumber();
        GeneratePermutations(rnd);
    }

    private void GeneratePermutations(RandomNumber rnd)
    {
        for (int i = 0; i < 256; i++)
        {
            p[i] = (short)rnd.Next(0, 256);
        }

        //repeat permutations.
        for (int i = 0; i < 512; i++)
        {
            perm[i] = p[i & 255];
            permMod12[i] = (short)(perm[i] % 12);
        }
    }

    // Skewing and unskewing factors for 2, 3, and 4 dimensions
    double F3 = 1.0 / 3.0;
    double G3 = 1.0 / 6.0;

    // This method is a *lot* faster than using (int)Math.floor(x)
    private int fastfloor(double x)
    {
        int xi = (int)x;
        return x < xi ? xi - 1 : xi;
    }

    private double dot(Grad g, double x, double y, double z)
    {
        return g.x * x + g.y * y + g.z * z;
    }

    // 3D simplex noise
    public float GetNoise(double xin, double yin, double zin)
    {
        double n0, n1, n2, n3; // Noise contributions from the four corners
                               // Skew the input space to determine which simplex cell we're in
        double s = (xin + yin + zin) * F3; // Very nice and simple skew factor for 3D
        int i = fastfloor(xin + s);
        int j = fastfloor(yin + s);
        int k = fastfloor(zin + s);
        double t = (i + j + k) * G3;
        double X0 = i - t; // Unskew the cell origin back to (x,y,z) space
        double Y0 = j - t;
        double Z0 = k - t;
        double x0 = xin - X0; // The x,y,z distances from the cell origin
        double y0 = yin - Y0;
        double z0 = zin - Z0;
        // For the 3D case, the simplex shape is a slightly irregular tetrahedron.
        // Determine which simplex we are in.
        int i1, j1, k1; // Offsets for second corner of simplex in (i,j,k) coords
        int i2, j2, k2; // Offsets for third corner of simplex in (i,j,k) coords
        if (x0 >= y0)
        {
            if (y0 >= z0)
            { i1 = 1; j1 = 0; k1 = 0; i2 = 1; j2 = 1; k2 = 0; } // X Y Z order
            else if (x0 >= z0) { i1 = 1; j1 = 0; k1 = 0; i2 = 1; j2 = 0; k2 = 1; } // X Z Y order
            else { i1 = 0; j1 = 0; k1 = 1; i2 = 1; j2 = 0; k2 = 1; } // Z X Y order
        }
        else
        { // x0<y0
            if (y0 < z0) { i1 = 0; j1 = 0; k1 = 1; i2 = 0; j2 = 1; k2 = 1; } // Z Y X order
            else if (x0 < z0) { i1 = 0; j1 = 1; k1 = 0; i2 = 0; j2 = 1; k2 = 1; } // Y Z X order
            else { i1 = 0; j1 = 1; k1 = 0; i2 = 1; j2 = 1; k2 = 0; } // Y X Z order
        }
        // A step of (1,0,0) in (i,j,k) means a step of (1-c,-c,-c) in (x,y,z),
        // a step of (0,1,0) in (i,j,k) means a step of (-c,1-c,-c) in (x,y,z), and
        // a step of (0,0,1) in (i,j,k) means a step of (-c,-c,1-c) in (x,y,z), where
        // c = 1/6.
        double x1 = x0 - i1 + G3; // Offsets for second corner in (x,y,z) coords
        double y1 = y0 - j1 + G3;
        double z1 = z0 - k1 + G3;
        double x2 = x0 - i2 + 2.0 * G3; // Offsets for third corner in (x,y,z) coords
        double y2 = y0 - j2 + 2.0 * G3;
        double z2 = z0 - k2 + 2.0 * G3;
        double x3 = x0 - 1.0 + 3.0 * G3; // Offsets for last corner in (x,y,z) coords
        double y3 = y0 - 1.0 + 3.0 * G3;
        double z3 = z0 - 1.0 + 3.0 * G3;
        // Work out the hashed gradient indices of the four simplex corners
        int ii = i & 255;
        int jj = j & 255;
        int kk = k & 255;

        int gi0 = permMod12[ii + perm[jj + perm[kk]]];
        int gi1 = permMod12[ii + i1 + perm[jj + j1 + perm[kk + k1]]];
        int gi2 = permMod12[ii + i2 + perm[jj + j2 + perm[kk + k2]]];
        int gi3 = permMod12[ii + 1 + perm[jj + 1 + perm[kk + 1]]];
        // Calculate the contribution from the four corners
        double t0 = 0.6 - x0 * x0 - y0 * y0 - z0 * z0; // change to 0.5 if you want
        if (t0 < 0) n0 = 0.0;
        else
        {
            t0 *= t0;
            n0 = t0 * t0 * dot(grad3[gi0], x0, y0, z0);
        }
        double t1 = 0.6 - x1 * x1 - y1 * y1 - z1 * z1; // change to 0.5 if you want
        if (t1 < 0) n1 = 0.0;
        else
        {
            t1 *= t1;
            n1 = t1 * t1 * dot(grad3[gi1], x1, y1, z1);
        }
        double t2 = 0.6 - x2 * x2 - y2 * y2 - z2 * z2; // change to 0.5 if you want
        if (t2 < 0) n2 = 0.0;
        else
        {
            t2 *= t2;
            n2 = t2 * t2 * dot(grad3[gi2], x2, y2, z2);
        }
        double t3 = 0.6 - x3 * x3 - y3 * y3 - z3 * z3; // change to 0.5 if you want
        if (t3 < 0) n3 = 0.0;
        else
        {
            t3 *= t3;
            n3 = t3 * t3 * dot(grad3[gi3], x3, y3, z3);
        }
        // Add contributions from each corner to get the final noise value.
        // The result is scaled to stay just inside [-1,1] (now [0, 1])
        return (float)(32.0 * (n0 + n1 + n2 + n3) + 1) * 0.5f; // change to 76.0 if you want
    }

    // get multiple octaves of noise at once
    public float GetOctaveNoise(double pX, double pY, double pZ, int pOctaves)
    {
        float value = 0;
        float divisor = 0;
        float currentHalf = 0;
        float currentDouble = 0;

        for (int i = 0; i < pOctaves; i++)
        {
            currentHalf = MathF.Pow(0.5f, i);
            currentDouble = MathF.Pow(2, i);
            value += GetNoise(pX * currentDouble, pY * currentDouble, pZ) * currentHalf;
            divisor += currentHalf;
        }

        return value / divisor;
    }
}